This invention relates to a method of non-destructively testing aluminum-to-copper welds and, more particularly, to a method of performing such testing by acoustic emission techniques.
When aluminum and copper parts are flash butt welded together, small quantities of relatively brittle copper-aluminum intermetallic compounds are usually formed at the joint interface. The quality of the weld depends to a large extent upon the thickness and dispersion of this deposit of intermetallic compounds. If this deposit is in the form of a continuous and relatively thick layer, the joint will be embrittled to such an extent that it may not be reliable under actual working conditions.
Heretofore, such joints have typically been tested by subjecting representative samples to a destructive bend test, referred to hereinafter as a 90.degree.-180.degree. bend test. In this bend test, a sample, in the form of a bar comprising copper and aluminum sections joined together by such a weld, is first bent at the weld joint until one section is angularly displaced by 90.degree. from the other and is then reversely bent until said one section is at 180.degree. to its previously-displaced position. If the sample can withstand such bending without significant debonding at the weld joint (e.g., less than 30% debonding), the weld is considered to have passed the test. But if significant debonding (i.e., 30 percent or more) does occur, a failure is indicated.
This bend test reveals much information on the thickness and distribution of the intermetallic compounds at the interface. Also, extensive testing has given a good correlation between bond test sampling and the reliability of similar welds throughout the anticipated lifetime of identical bars made in the same way as the tested bar.
But the destructive nature of the 90.degree.-180.degree. bend test is a definite disadvantage. The test specimen is rendered unusable by such test, and any bar that is to be actually used in a working environment cannot be subjected to an actual bend test.